with some Remarks on the Nature of the Spongise Marinse. 391 



ing within the cells or canals of this kind of Sponge, is one, I believe, at pre- 

 sent unknown, and one of a very remarkable form and character. It is in 

 appearance not unlike a wingless Aphis ; it varies somewhat in size, probably 

 according to its age ; is apterous and of a green colour, much resembling that 

 of the Sponge itself, but is occasionally rather more marked with brown. It 

 seems to inhabit this Freshwater Sponge alone, for I do not recollect to have 

 noticed it in any other production ; it burrows in it, feeds upon it, eating away 

 large pieces of it ; coming forth from its hole, it is often seen walking over 

 the surface of the mass, and retreats, particularly when disturbed, within the 

 canals again. Possessing on the under part of its body certain membranaceous 

 appendages, which are clearly a sort of branchiae or gills, it makes use of them 

 for the purpose of breathing. Whilst it effects the function of respiration the 

 insect remains within its hole perfectly still, but only keeps rapidly vibrating 

 these gills or branchial appendages, by means of which currents are produced 

 in the water near to the spot where it is lodged. 



To this insect, then, I attribute for the most part those currents which I 

 have observed flowing into, and out from, the pores or canals of the Spongilla 

 Jluviatilis ; or else to the same cause, namely, to the process of respiration 

 being carried on by some moUuscan, or insect, hid within and inhabiting that 

 individual specimen ; for I have always succeeded in discovering, whenever I 

 have noticed similar currents or streams in the water, the presence either of 

 some parasitical insect, or of some molluscan, upon which the Sponge has 

 grown and afterwards entirely invested. Moreover, I have never yet been 

 able to perceive these currents in any living mass of this Freshwater Sponge 



Sponge insects are aquatic and furnished with gills, which no imago that I am acquainted with pos- 

 sesses. If regarded as larvse, it is difficult to conceive even to what order of insects they belong, the 

 structure of the mouth being unlike every group having aquatic larvae ; in some respects they are al- 

 lied to the larvae of the Hemerobii, which have long mandibles and maxillae, but these are all terres- 

 trial. We are too well acquainted also with the larvae of the Trichoptera to regard them as belonging 

 to that order ; and in the Neuroptera we know the transformations of all the groups. There is, how- 

 ever one anomalous genus, Acentropus, of which even the order is doubtful ; and as we are ignorant 

 of its early stages, it may possibly belong to that." 



Having kept in a basin of fresh water for many days together specimens of the Spongilla wherein 

 were some of these insects, and having never observed them even beginning to transform, I am very 

 much inclined to consider that they have attained their perfect state. A short notice of this insect is 

 given in the Mag. Nat. Hist., vol. iii. N. S. p. 200, No. for April, 1839. 

 VOL. XVIII. 3 F 



